Phosphor-converted white light-emitting diodes (pc-white LEDs) have attracted considerable attention as a new generation light source since the first commercial GaN chip was invented in 1990s. A pc-white LED can be regarded as a sophisticated system including a number of components made of a variety of materials. An understanding of the behavior of its component parts is helpful to gain a comprehensive insight of the failure of the pc-white LED itself. For this reason, issues related to materials and reliabilities of the LED key components such as LED chip, phosphor, encapsulant, lead frame, and interface are discussed in this chapter.

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Due to low power consumption, long lifetime and many other advantages, Light-emitting Diode (LED) has increased dramatically all over the world. Chip Scale Package (CSP) LED is a new LED package with small size, high current, and high reliability. For the CSP LED with smaller size and lower thermal resistance, phosphors and silicone are usually combined as the phosphors/silicone composite and prepared by using a high temperature cure process. However, for those CSPs which are not sufficiently cured, their reliability under a harsh environment (e.g. high temperatures and high humidity) will obviously decrease. In this study, the influence of temperature and ultraviolet light on the cure process of phosphor/silicone composites is studied and an optimal cure process is extracted accordingly. According to the cure experiment under different conditions, the results show that ultraviolet light and phosphor can promote the cure reaction of silicone. With the increase of ultraviolet light intensity and phosphor mass fraction, the cure rate of the silicone and phosphor/silicone composite is greatly increased as well.

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A typical cement-based exterior wall consists of a top coat, a base coat, an insulation layer, a steel frame and an interior layer. The top coat and the base coat are often made of mortar. Efflorescence at the surface of the top coat is a critical problem from the aesthetic point of view. The efflorescence can be caused by leaching of Ca(OH)2 from the top coat and the base coat. This paper aims to mitigate the efflorescence of the top coat by incorporating metakaolin.
Cement in the top coats is substituted with metakaolin at different substitution rates (i.e. 0 - 20% by mass of cement). Mechanical properties of the top coats are measured. The extent of the efflorescence of two-layer specimens (i.e., top coat + base coat) is quantified by image analysis. The content of Ca(OH)2 and the porosity of the top coats are determined for explaining the mechanism of mitigation of efflorescence by incorporating metakaolin. The results show
that the compressive strength and the flexural strength of the top coats are improved when the substitution rates of metakaolin are lower than 15%. The metakaolin results in lower porosity and lower content of Ca(OH)2 in the tops, due to the filler effect and the pozzolanic reaction of metakaolin. The substitution of metakaolin for cement can effectively mitigate the
efflorescence of the top coats, and the efficiency of metakaolin increases with the substitution rate (from 0 to 20%). The conclusion is that metakaolin is a promising material for mitigating efflorescence of cement-based exterior wall.@en